1. Field of the Invention
This invention relates to a filter of water for keeping aquarium fishes such as goldfishes, tropical fishes, saltwater fishes, and the like.
2. Description of the Prior Art
A conventional filter used inside a water tank for keeping goldfishes, tropical fishes, and the like blows air into water by an air pump or the like to generate a water flow, and filtrates the water in the tank by feeding the water flow as a whole through a filter material. If the flow velocity of the water passing through the filter material is too great, however, aerobic bacteria that decompose organic matters such as chlorella, residual bait and droppings of fishes, and the like, can not be propagated, so that the water quality would be deteriorated. If the flow velocity is reduced, on the other hand, oxygen can not sufficiently be supplied into the water, and an air pump for supplying oxygen must be used additionally. If the filter material gets clogged, the water flow becomes weak and will invite the insufficiency of oxygen in the water.